While premature deaths due to cancer and heart disease are projected to decrease for most Americans from 2017 to 2030, premature deaths due to suicide are expected to increase for all groups. U.S. military Veterans exhibit suicide rates that are approximately twice as high as those of non-Veterans. Accordingly, the Veterans Administration has assigned the highest priority to the reduction of suicide rates among those that have served in the U.S. military. Importantly, the VA has leveraged its status as the largest integrated health system in the U.S., with a unified electronic health record covering approximately 9,000,000 patients, to develop a state-of- the-art predictive model, REACH VET, designed to identify patients at elevated risk for suicide. Inside and outside the VA, a key domain that has received little attention is the detection of acute risk elevation signaling a need for immediate intervention. This is understandable given extremely low base rate of completed suicide and the challenges this presents to surveillance. New, inexpensive, fully automated, commercial sleep monitoring devices now offer the possibility of obtaining nightly objective sleep and heart rate data which may substantially improve the temporal precision of suicide surveillance. A large body of literature has established strong associations between subjective and objective sleep disturbances and suicidal ideation and completion. As well, two large epidemiological studies have demonstrated associations between elevated basal heart rate and completed suicide. This research will assess whether nightly objective sleep scheduling and heart rate data can 1) distinguish, at the group level, U.S. military Veterans diagnosed with PTSD and identified as high- risk for suicide from Veterans with PTSD but at low risk for suicide, and 2) predict weekly variation in suicidal ideation in the high-risk group. The study design extends pilot and published work by Drs. Woodward, Pigeon, Bernert, and Khan. Forty Veterans with PTSD recruited through the REACH VET and local VAPAHCS high- risk lists and 40 Veterans with PTSD but free of known suicide risk will be monitored in their homes for eight and four weeks, respectively. In the event of positive results, a larger multisite trial would offer an opportunity to integrate actuarial and sleep data to further improve suicide surveillance.